System and method for controlling errors in computed tomography number

1. A method for creating computed tomography (CT) images comprising:

acquiring or accessing sinogram data;

determining a photon count for the sinogram data;

generating unbiased sinogram data from the sinogram data using an unbiased estimator and the photon count; and

reconstructing a CT image from the unbiased sinogram data.

2. The method of claim 1 , wherein determining the photon count includes determining an actual photon count at each of a plurality of detector elements across a field of view.

3. The method of claim 1 , wherein determining the photon count includes determining a photon count at all non-zero count detector elements.

4. The method of claim 1 , further comprising correcting for detector elements indicating a zero photon count.

5. The method of claim 4 , wherein correcting for detector elements indicating a zero photon count includes creating a respective macro-pixel for each detector element indicating a zero photon count and calculating a corrected sinogram for the macro-pixel.

6. The method of claim 1 , wherein generating the unbiased sinogram includes selecting coefficients to cancel out statistical biases of terms in a mathematical expansion relating the sinogram data to the photon count.

7. The method of claim 1 , further comprising generating the unbiased sinogram data using at least one of:

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wherein {tilde over (y)} i , is the unbiased sinogram data, y i , is the sinogram data, and N i is the photon count.

8. A medical imaging system comprising:

an x-ray source configured to deliver x-rays to an object as the x-ray source is rotated about the object;

a detector having a plurality of detector elements configured to receive the x-rays and generate sinogram data therefrom;

a controller configured to control the x-ray source to deliver the x-rays and to receive the sinogram data from the detector;

a processor configured to:

determine a photon count for the sinogram data for a plurality of detector elements;

generate unbiased sinogram data from the sinogram data using an unbiased estimator and the photon count; and

reconstruct a CT image from the unbiased sinogram data.

9. The system of claim 8 , wherein the processor is further configured to determine the photon count as an actual photon count at each of the plurality of detector elements.

10. The system of claim 8 , wherein the processor is further configured to determine the photon count by determining a photon count at all detector elements without a zero photon count.

11. The system of claim 8 , wherein the processor is further configured to correct for detector elements indicating a zero photon count.

12. The system of claim 11 , wherein the processor is further configured to correct for detector elements indicating a zero photon count by creating a respective macro-pixel for each detector element indicating a zero photon count and calculating a corrected sinogram for the macro-pixel.

13. The system of claim 8 , wherein the processor is further configured to generate the unbiased sinogram by selecting coefficients to cancel out statistical biases of terms in a mathematical expansion relating the sinogram data to the photon count.

14. The system of claim 8 , wherein the processor is further configured to generate the unbiased sinogram data using at least one of:

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wherein {tilde over (y)} i ; is the unbiased sinogram data, y i , is the sinogram data, and N i is the photon count for the plurality of detector elements.

15. A method comprising:

controlling a computed tomography system to acquire biased sinogram data (y i );

determining a photon count (N i ) from the sinogram data;

generating unbiased sinogram data ({tilde over (y)} i ) using at least one of:

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wherein y i ; is the sinogram data, and N i is the photon count for the plurality of detector elements; and

reconstructing an image from the unbiased sinogram data.

16. The method of claim 15 , wherein determining the photon count includes determining a photon count for each element of the detector used to acquire the sinogram data having a non-zero count.

17. The method of claim 15 , further comprising correcting for each element indicating a zero photon count.

18. The method of claim 17 , wherein correcting for each detector element indicating a zero photon count includes creating a respective macro-pixel for each detector element indicating the zero photon count and calculating a corrected sinogram for the macro-pixel.